Learn Finnish: Me olemme nyt eläintarhassa.

Even though a zoo is outdoors, Finnish treats it as an enclosed, defined space—very similar to how a park (puisto) works. Because you are within its boundaries, you use the inessive -ssa (in/inside) rather than the adessive -lla (on/at) to say you are at the zoo.

Do I need to include the pronoun me (we) at the beginning of the sentence?

Not strictly! Because the verb olemme already clearly means "we are," you can drop the pronoun and just say Olemme nyt eläintarhassa. Including Me just adds a bit of emphasis or makes the sentence feel a bit more grounded, which is very common.

Is it mandatory to put nyt (now) right after the verb?

No, Finnish word order is flexible. You could also say Me olemme eläintarhassa nyt, putting the time word at the end just like in English. However, placing short adverbs of time directly after the verb is an extremely common and natural-sounding pattern in Finnish.